Preparation of tetraethylthiuramdisulfide



Jan. 15, 1957 J, c. COUNTS EIAL PREPARATION OF TETRAETHYLTHIURAMDISULFLIDE INVENTORS JAMES C. COUNTS ROBERT T. NELSON WILLIAM R. TRUTNA DIETHYLDITHIOCARBAMATE 22 CHLORINE SODIUM ATTORNEY PREPARATION OF TETRAETTH SULFIDE Application June 1, 1954, Serial No. 433,544 6 Claims. (Cl. 260-567) This invention relates to the manufacture of tetraethylthiuram disulfide. More particularly, it relates to processes especially adapted for obtaining tetraethylthiuram disulfide by the oxidation of a salt of diethyl dithiocarbamic acid using gaseous chlorine.

A variety of processes have heretofore been suggested for oxidizing salts of dialkyl dithiocarbamic acid to tetraalkylthiuram disulfides: Adams U. S. 1,782,111 suggests oxidation using hydrogen peroxide in the presence of sulfuric acid; Kline U. S. 1,876,059 uses polythionates as oxidizing agents; Olin et a1. U. S. 2,325,194 discloses as oxidizing agents ammonium persulfate, nitrous acid and alkyl nitrites; Cooper U. S. 2,375,083 suggests the use of chlorine or bromine following a special technique which requires introduction of the halogen into the atmosphere above the surface of a solution of a water soluble salt of the dialkyl dithiocarbamic acid.

Those of the aforementioned patents that specifically disclose the preparation of tetraethylthiuram disulfide fail to suggest that there are any problems involved of the production of that compound that do not exist in the preparation of the lower homologue tetramethylthiuram disulfide. We have found, however, at least as to the use of chlorine as the oxidizing agent, that it is commercially impractical to use the same process for tetraethylthiuram disulfide as for tetramethylthiuram disulfide, changing only the starting material from a dimethyl dithiocarbamate to a diethyl dithiocarbamate.

In the oxidation of a dimethyl dithiocarbamate, one can obtain good quality tetramethylthiuram disulfide product in high yield using relatively. high concentrations of chlorine in thereaction zone, e. g., one volume of chlorine for every to 25 volumes of diluent gas. Using the same conditions for the preparation of tetraethylthiuram disulfide, the yield'is relatively low and the product-quality poor.

We have now found that tetraethylthiuram disulfide of commercially attractive quality can be made in high yield using a chlorine oxidation process provided the chlorine is extremely diluted with an inert gas before contacting the diethyl dithiocarbamate to be oxidized, and we have discovered practical methods for conducting the reaction on a commercial basis under such conditions of extreme dilution.

In the drawing, Figure 1, shows diagrammatically a process for use in the practice of a preferred embodiment of the invention; and in Figure 2 there is shown in semidiagrammatical form an apparatus adapted for use in the practice of another preferred embodiment of the invention.

Having reference to Figure 1, there will be seen a series of separators 1a, 1b, and 10, into which reacting mass flows from lines 2a, 2b, and 20 respectively.

Chlorine which serves as the oxidizing agent is fed into the process from main line 3 at a plurality of points in the system via lines 4, 4a, 4b, and 40.

Air, as shown in the drawing, is the preferred gaseous diluent for economic reasons but other inert gases such as nitrogen can be used if desired. Inthe embodiment shown in Figure 1, air is supplied thru pipeline 5 for admixture in pipeline 6 with chlorine introduced thru pipeline 4.

An aqueous solution of the. salt of diethyl dithiocarbamic acid which is to be oxidized is fed into the system thru pipeline 7 for initial mixing and reaction with chlorine in pipeline 8 and vertical pipeline 2a. Sodium diethyl dithiocarbamate, which is shown in the drawing, is the preferred salt for economic reasons but it will be appreciated that other water soluble salts such as the ammonium and potassium salts of diethyl dithiocarbamic acid can alsobe used. The inert gas and chlorine are introduced into pipeline 6 in the proportions of at least volumes of inert gas for each volume of gaseous chlorine and more preferably from about 150 to 400 volumes of inert gas per volume of gaseous chlorine. In general, the yield and quality of product obtained are improved as the air to chlorine ratio is increased. However, ratios of greater than 400 to 1 offer little additional advantage along those lines and the equipment and operating costs per unit of product increase rapidly because of the large volumes of gas to be handled. On the other hand, use of substantially less than 75 volumes of inert gas per volume of gaseous chlorine seriously affects adversely both yield and quality of product.

The aqueous solution of the diethyl dithiocarbamate as introduced thru pipeline 7 has, according tothe preferred processes of this invention, a pH Within the range of about 9 to 11. The concentration of dithiocarbamate in this solution can be varied widely up to the saturation point, i. e., up to about 40 to 50%. At the higher concentrations, the slurries formed in the equipment as tetraethylthiuram disulfide precipitates are inconveniently thick and tend to interfere with the proper flow of the material. Therefore, it is preferred tooperate at a dithiocarbamate feed concentration in the order of 5 to 20% by weight altho thereis no serious objection to use of lower concentrations if equipment and production requirements permit. There is, however, an advantage in using concentrations, in the higher portion of the latter range, say in the order of 15 to 20% by weight, or higher if flowability is not a problem in the particular equipment used, because such higher concentrations make possible the use of lower inert gas to chlorine ratios than would otherwise be necessary with less concentrated solutions to obtain product of equal quantity in equally high yield.

The relative ratio and amounts of gaseous component to aqueous solution brought together in pipeline 8 can be varied widely and in general, the proportion will be from about 0.5 to cubic feet of gas per gallon of solution and the amount of gas introduced will be sutficient to provide in vertical pipe 211 a linear gas velocity of approximately 5 to feet per second. Using apparatus of the type illustrated by Figure l, in which 2a, 2b, and 20 represent vertical pipes in which a major part of the oxidation reaction occurs, we have found that excellent results are obtained using gas toliquid ratios in the order of from about 0.5 to 30, and preferably 0.5 to 5, cubic feet of gas per gallon of liquid and in such quantity that there is obtained a so-called slug-type flow such as is observed in the common usage of the air lift method for transporting liquids upward thru vertical pipes. In the purpose of securing the lower ratios of gas to liquid a line connecting lines 9 with the bottoms of lines 2 may be desirable. This results in recirculation of liquid in each stage thus permitting lower ratios of gas to liquid than are present in the feed streams. f

Because of the extreme chlorine dilution employed in practicing the processes of the investion and the other flow conditions inherent in the operation, only a portion of the chlorine stoichiornetrically required to oxidize all the diethyl dithiocarbamate introduced via. line 7 is introduced thru pipeline 4. Ideally, the operation is adiusted so that all or at least a major quantity of the chlorine introduced thru pipeline 4 is consumed in the oxidation reaction which occurs in pipeline 2a.

The aqueous reacting mass flows into separator 1a wherein the aqueous portion, now containing some suspended solid tetraethylthiuram disulfide, falls and is withdrawn thru pipeline 9a, and the unreacted gaseous component consisting almost entirely of air or other inert gas and little or no chlorine is withdrawn overhead thru pipeline 10a.

The separated unreacted gaseous component Withdrawn thru pipeline 10a is refortified with chlorine supplied thru pipeline 4a. Ordinarily sufficient chlorine is introduced thru pipeline 2a to replace the amount consumed in the preceding oxidation reaction but the amount can, if desired, be varied provided it is limited so that the gaseous mixture passing into and thru pipeline 11a contains at most about one volume of gaseous chlorine for each 75 volumes of inert gas.

The refortified gaseous mixture flowing thru pipeline 11a is then admixed with the separated aqueous reacting mass from pipeline 9a to efiect further oxidation of unreacted diethyl dithiocarbamate in vertical pipeline reactor 2b.

The aqueous reacting mass flows from pipeline 2b into separator 1b wherefrom the aqueous component is withdrawn thru pipeline 9!) and the aseous component thru pipeline 10b in the manner described heretofore with reference to separator 1a and its associated equipment which represented the first stage of the three stages illustrated in Figure 1.

In the second stage as in the first sta e. the withdrawn unreacted aseous component is refortified w th chlorine. supplied this time thru pipeline 4h. care again being exercised to limit the amount of chlorine to less than one volume for each 75 volumes of inert gas. The refortified gaseous mixture is admixed with the separated aqueous reacting mass to effect further oxidation in vertical react r 2c.

The aqueous reacting mass from 20 flows into the third separator 10 wherein separation of the aqueous and aseous components occurs as in the previous two sta es. The withdr wn aseous component p ssin thru ipeline 10-: for ref rtificatinn with chlorine introduced thru pi eline 4c and the resulting dilute chlorine as being admixe with the separated aqueous reacting mass in line 12 wherefrorn it passes t ru one or m re rocessin sta es like those of the three illustrated in the fiuure u til all or s bstantially all f the dieth l dithincarh rnate has reacted.

The vield and oualit of product improves somewh t as the number of rea tion or roces in st es increases since an increase in the number of Stan-es perm s in- Cre se in the avera e concentration at which the d ethvl dithioc rbam te salt can be reacted. Also. less inert has h s t be su plied to the svstem per unit of roduct as the number of sta es is increased. For practical purposes. four to fift n sta es are normally used.

The liouid component withdrawn from the final sens: rator in the series contains the desired tetraethvltbiurqm disulfide in suspensio in solid particulate form. The tetraethvlthiuram disulfide is separated from the aqueous liquid by means of a filter or other apparatus adapted for separating solids from liquids such as a centrifuge.

Having reference to Figure 2 in the drawing, there will be seen in semi-diagrammatical form, and partly in section, another apparatus adapted for use in practicing processes of the invention. There will be seen as the principal unit a tower 15 divided into sections by a plurality of sieve plates 16, and containing downpipes 17 adapted for transferring liquid overflow from one sieve plate to the next lower plate. In addition, a means for a solid plate 18 is disposed between each sieve plate and a pipeline 19 bypass the solid plates. Thus the tower 15 is a somewhat modified version of what is commonly known as a sieve plate or perforated plate column and conventionally used as a refining or fractionating column.

The chlorine is introduced thru pipeline 29 and a portion of the total requirement is mixed with air or other inert gas from pipeline 21 and introduced into the base of the tower.

An aqueous solution of the diethyl dithiocarbamate to be oxidized is introduced into the top of the tower thru pipeline 22.

The gas mixture introduced thru pipeline 21 passes upward thru the openings in plates 16, which plates are shown in the drawing as sieve plates but can alternatively be of conventional design such as bubble cap plates, then passes thru a layer of liquid component on each plate, which component flows across each plate and then downward to the next lower plate where additional oxidation takes place.

Additional chlorine is introduced via pipelines 23a, 2312, etc. as required to maintain chlorine in the gaseous mixture passing thru the liquid layers on the plates, care being taken to avoid having the chlorine concentration passing thru the plates be substantially in excess of one volume of chlorine for each volumes of inert gas.

The oil gas is withdrawn from the column thru pipeline 24 and the liquid component, containing precipitated tetraethylthiuram disulfide, is removed from the base of the column thru pipeline 25. The product is recovered from the efliuent liquid component by conventional methods such as filtration or by centrifuging.

Referring to other details in Figure 2, it will be seen that weirs 26 are employed to maintain the desired liquid level on the sieve plates and splash bafiles 27 are used to prevent flow of undue amounts of foam into downpipes 17. Each solid plate 18 is equipped with a drain line 28 but it will be understood that in normal operation the flow rates are such that there is substantially no leakage thru the sieve plates onto the solid plates.

It will be understood that the comments made heretofore concerning the process of Figure 1 with regard to the concentration of diethyl dithiocarbamate in the aqueous solution, the chlorine-inert gas proportions and amounts, number of plates or stages, and like variables are similarly applicable to processes operated in an apparatus of the kind illustrated in Figure 2.

The oxidation reaction is exothermic and the processes of the invention are carried out preferably so that the temperature of the liquid component does not exceed about 60 C. This is conveniently done by introducing the reactants at room temperature or below if necessary. Preferably, the liquid component is maintained within the temperature range of 10 C. to 40 C. thruout the process.

Preferably the aqueous portion of the reacting mass is maintained within the range of about pH 5 to pH ll thruout the process. The pH of the solution drops as the reaction proceeds. The process can be operated either with or without the addition of an alkali such as sodium bicarbonate. The use of an alkali may sometimes be preferred to avoid too low pH during the reaction with subsequent yield loss and to avoid a sudden drop in pH upon completion of the reaction which would result in liquors corrosive to subsequent processing equipment. For example, 5% sodium bicarbonate solution in water can be metered into the liquid component in the process at an intermediate point in the process, e. g. when 30% to of the dithiocarbamate has reacted, in amount sufficient to maintain the exit pH at 5 to 7.

While the invention has been described with particular reference to the embodiments shown in the drawing and described in the foregoing detailed examples, it will be apparent to one skilled in the art that various modifications can be made in the manipulative techniques or apparatus design for carrying out processes of the inven tion, the essential feature of which is that the oxidation be eifected by contacting an aqueous solution of a diethyl dithiocarbamate with an extremely dilute chlorine gas, namely, one which contains at least 75 volumes of inert gas for each volume of gaseous chlorine.

Thus, instead of having vertical reactors 2a, 2b, and 2c, as shown in Figure 1, one could use horizontal reactors at a slight sacrifice in product, yield, and quality. Indeed, in addition to the continuous processes shown, processes of the invention can be carried out batchwise by bubbling the very dilute chlorine gas directly into a body of the aqueous component in a vessel but such practice is relatively unattractive for commercial operation. Other variations in details without departing from the scope of the invention described and claimed will be apparent to those skilled in the art.

In order that the invention may be better understood, the following detailed examples are given in addition to the examples already given above.

Example 1 Using an 8-plate tower of the kind illustrated in Figure 2, there is fed into the bottom of the tower at about 20 C. a gaseous chlorine-air mixture containing about 260 volumes of air per volume of chlorine. The gaseous mixture is passed thru the tower at a rate of about 2.2 feet per second.

A 9% solution of sodium diethyl dithiocarbamate in water, pH 10.5 and temperature about 10 C., is metered into the top of the tower at a rate of about one gallon of said solution for each 50 cubic feet of air fed into the bottom of the tower.

About 96% of the chlorine introduced into the bottom of the tower is consumed in contacting the liquid component on the bottom plate and an additional quantity of chlorine is introduced into the zone beneath the next plate to restore the air: chlorine volume ratio to about 260:1; the chlorine consumption is repeated on each plate and chlorine is likewise introduced beneath each plate to maintain the 260:1 ratio.

The liquid component withdrawn from the bottom plate of the column is at a temperature of about 30 C. and at a pH of about 5.5. It contains a suspension of tetraethylthiuram disulfide precipitate. This precipitate is removed by filtration, washed, and dried. The dried product is 99% tetraethylthiuram disulfide and has a melting point of 69.0 C. The process provides a yield of 92% based on the sodium diethyl dithiocarbamate and 85% based on the chlorine.

Example 2 An 8.95%, by weight, water solution of sodium diethyl dithiocarbamate, pH 10, is metered into the end of a 3- feet long, /3 inch diameter, glass pipe at a rate of 0.28 gaL/min. A mixture of chlorine gas and air in an air to chlorine volume ratio of about 198 to 1 is metered into the glass pipe three inches downstream of the point where the liquid enters. The chlorine rate is 0.038 gram mole per minute and the air rate is 6.0 standard cubic feet per minute.

During the passage of the fluids thru the glass pipe, substantially all of the chlorine is consumed in the liquid. The gas and liquid discharge from the end of the pipe into a glass liquid-gas separator. The liquid, which now contains some precipitated tetraethylthiuram disulfide and the unreacted portion or" the sodium diethyl dithiocarbamate, is discharged from the bottom of the separator into another 3-feet long, inch diameter, glass pipe. The oil? gas is taken oil the top of the separator. Chlorine, at a rate of 0.038 gram moles per minute, is metered into the ofi-gas stream and the mixture of off-gas and chlorine is fed to the second glass pipe. This process is sodium diethyl dithiocarbamate feed is unreacted; 88%

of the chlorine feed is accounted for by the product tetraethylthiuram disulfide.

Example 3 2340 parts by weight of a 15.6%, by weight, water solution of sodium diethyl dithiocarbamate are charged to a glass reaction vessel. Chlorine, diluted with air in a ratio of one volume of chlorine to 380 volumes of air, is then bubbled below the surface of the agitated sodium diethyldithiocarbamate solution at a rate of 0.23 part by weight of chlorine per minute until a total of 73.0 parts by weight of chlorine have been introduced. The pH of the solution gradually falls from an initial pH of 10.3 as the chlorine is added; and 56 parts by weight of a 5% solution of sodium bicarbonate in water are added to keep the pH from falling below 7.0. Throughout the addition of chlorine the temperature of the reaction mass is held at 2526 C.

The precipitated tetraethylthiuram disulfide is filtered, washed, and dried yielding 288 parts by Weight of 99.4% tetraethylthuiram disulfide. The melting point of the dried product is 68.3 C. 90% of the sodium diethyl dithiocarbamate reacts to form tetraethylthiuram disulfide and 5.5% remains unreacted.

We claim:

1. A process for the preparation of tetraethylthiuram disulfide which comprises oxidizing a salt of diethyl dithiocarbamic acid by mixing an aqueous solution of said salt with gaseous chlorine diluted with an inert gas so that there is present during the oxidation reaction at least 75 volumes of said inert gas per volume of gaseous chlorine.

2. A process for the preparation of tetraethylthiuram disulfide which comprises mixing an aqueous solution of a salt of diethyl dithiocarbamic acid with gaseous chlorine diluted with a quantity of inert gas to provide at least 75 volumes of said inert gas per volume of gaseous chlorine, said chlorine constituting substantially less than the stoichiometric amount required to oxidize all of said salt of diethyl dithiocarbamic acid to tetraethylthiuram disulfide, whereby a portion of said salt is oxidized to tetraethylthiuram disulfide and chlorine is consumed, then separating the aqueous reacting mass from unreacted gaseous component, and mixing said separated aqueous reacting mass with an additional quantity of gaseous chlorine diluted with a quantity of inert gas to provide at least 75 volumes of said inert gas per volume of gaseous chlorine to oxidize another portion of said salt of diethyl dithiocarbamic acid to tetraethylthiuram disulfide.

3. A process for the preparation of tetraethylthiuram disulfide which comprises oxidizing a salt of diethyl di thiocarbamic acid by mixing an aqueous solution of said salt with gaseous chlorine diluted with an inert gas so that there is present during the oxidation reaction at least 75 volumes of said inert gas per volume of gaseous chlorine,

- said chlorine being brought into contact with said aqueous solution in substantially less than the stoichiometric amount required to oxidize all of said salt of diethyl dithiocarbamic acid to tetraethylthiuram disulfide, whereby a portion of said salt is oxidized to tetraethylthiuram disulfide and gaseous chlorine is consumed, then separating the aqueous reacting mass from unreacted gaseous component, refortifying said separated unreacted gaseous component with chlorine to provide a gaseous mixture containing at most about one volume of gaseous chlorine for each 75 volumes of inert gas in said gaseous mixture, then mixing said reforti'fied gaseous mixture with .saidseparated aqueous reacting mass to efiect oxidation of salt of diethyl dithiocarbamic acid in said aqueous reacting mass to tetraethylthiuram disulfide, and repeating said separating, refortifying and mixing steps as required to oxidize substantially all of the salt of diethyl dithiocarbamic acid to tetraethylthiuram disulfide.

4. A process, according to claim 3, in which sodium diethyl dithiocarbamate is the salt of diethyl dithiocarbamic acid used and substantially throughout the duration of the oxidation reaction the aqueous reacting mass is maintained at about pH 5 to pH 11 and at a temperature of from about 10 C. to 40 C.

5. A continuous process for the preparation of tetraethylthiuram disulfide which comprises continuously feeding an aqueous solution of a salt of diethyl dithiocarbamic acid into an oxidation zone which is the first of a series of oxidation zones and continuously -feeding into the last of the oxidation zones in said series a gaseous mixture consisting essentially of gaseous chlorine, in amount substantially less than the stoichiometric amount required to oxidize all of said salt of diethyl dithiocarbamic acid to tetraethylthiuram disulfide, and at least 75 volumes of an inert gas per volume of gaseous chlorine, maintaining in each oxidation zone an aqueous mass containing a lesser content of said salt of diethyl dithiocarbamic acid than in the next preceding zone by oxidizing a portion of said salt of diethyi dithiocarbamic acid to tetraethylthiuram disultide in each zone by mixing with the said aqueous mass .in each of said zones avgase'ous chlorine-containing mixture consisting essentially of chlorine and inert .gas, continuously passing aqueous mass so treated from each oxidation zone to the next succeeding oxidation zone, the gaseous chlorine-containing mixture which is mixed with the aqueous mass in each zone, preceding the aforementioned last zone, consisting essentially of the gaseous eiiluent from the succeeding zone to which gaseous effluent there has been added chlorine to replace, at least in part, chlorine consumed in the said succeeding zone; and withdrawing from the last of said oxidation zones an aqueous mass in which substantially all of the salt of diethyl dithiocarbamic acid has been oxidized to tetraethylthiuram disulfide.

6. A process according to claim 5 in which sodium diethyl dithiocarbamate is the salt of diethyl dithiocarbamic acid used and substantially throughout the duration of the oxidation reaction the aqueous reacting mass is maintained at about pH 5 to pH 11 and ate temperature of from about 10 C. to 40 C.

References Cited in'the file of this patent UNITED STATES PATENTS 1,782,111 Adams et a1 Nov. 18, 1930 1,796,977 Bailey Mar. 17, 1931 2,286,690 Sibley June 16, 1942 2,375,083 -Cooper May 1, 1945 

1. A PROCESS FOR THE PREPARATION OF TETRAETHYLTHIURAM DISULFIDE WHICH COMPRISES OXIDIZING A SALT OF DIETHYL DITHIOCARBAMIC ACID BY MIXING AN AQUEOUS SOLUTION OF SAID SALT WITH GASEOUS CHLORINE DILUTED WITH AN INERT GAS SO THAT THERE IS PRESENT DURING THE OXIDATION REACTION AT LEAST 75 VOLUMES OF SAID INERT GAS PER VOLUME OF GASEOUS CHLORINE. 